In drilling wells for oil and gas exploration, understanding the structure and properties of the associated geological formation provides information to aid such exploration. True formation resistivity is a key petrophysical parameter that helps petrophysicists to characterize and develop a reservoir. A resistivity measurement presents an electrical property of formations surrounding the logging tools, where different formations have distinct and unique resistivity readings. For example, a salt water formation presents a low resistivity reading and an oil reservoir presents a high resistivity reading. A continuous resistivity log allows petrophysicists to recognize formation geology and to develop a good wellbore placement program for maximum oil production in the reservoir. However, a resistivity measurement is often problematic in layered formations, especially while the logging tool is near the boundary between the layers, each with different resistivity value. Such boundary effects, known as polarization horn effects, can produce significant responses to conventional propagation electromagnetic (EM) wave tools and unrealistic resistivity reading with very high value may be measured. Consequently, misinterpretation of formation geology may occur based on such resistivity measurements.
In general, one-dimensional (1D) inversion is often used to eliminate such horn effects and explore the true formation resistivity profiles. Inversion operations can include a comparison of measurements to predictions of a model such that a value or spatial variation of a physical property can be determined. In inversion, measured data may be applied to construct a model that is consistent with the data. For example, an inversion operation can include determining a variation of electrical conductivity in a formation from measurements of induced electric and magnetic fields. Other techniques, such as a forward model, deal with calculating expected observed values with respect to an assumed model. In zero-dimensional (0D) inversion, there is no variation in the formation, such as in a homogenous formation. In 1D modeling, there is variation in one direction such as a formation of parallel layers. In two dimensional (2D) modeling, there is variation in two directions. In three dimensional (3D) modeling, there is variation in three directions. However, inversion schemes can be complicated and can have several uncertainties, such as initial formation model, number of input signals for the inversion, etc., that may cause different inverted results. The usefulness of such traditional measurements and inversion analysis may be related to the precision or quality of the information derived from measurements and processes to evaluate the information.